1. Field of the Invention
This invention relates to stepper exposure systems and more particularly to correction methods and apparatus therefor.
2. Description of Related Art
U.S. Pat. No. 4,823,012 of Kosugi for "Step and Repeat Exposure Apparatus Having Improved System for Aligning" describes alignment marks provided in association with neighboring fields on a wafer which are to be exposed to a reticle pattern in sequence.
U.S. Pat. No. 4,982,227 of Suzuki for "Photolithographic Exposure Apparatus with Multiple Alignment Modes" shows a method for alignment using multiple alignment modes by adapting an alignment method by a sample alignment prior to the exposure operation. The alignment modes examine multiple sized fields.
U.S. Pat. Re. 33,836 of Resor, et al. for "Apparatus and Method for Making Large Area Electronic Devices, Such as Flat Panel Displays and the Like, Using Correlated, Aligned Dual Optical Systems" shows an alignment method for substrates (displays not chips) that includes a means for aligning images.
U.S. Pat. No. 5,444,538 of Pellegrini for "System and Method for Optimizing the Grid and Intrafield Registration of Wafer Patterns" describes measurement of overlay misregistration and a method for optimizing the (grid) interfield and intrafield registration of dies.
U.S. Pat. No. 5,655,110 of Krivokapic et al. for "Method for Setting and Adjusting Process Parameters to Maintain Critical Dimensions across each Die of Mass-Produced Semiconductor Wafers" teaches a method for adjusting alignment parameters to optimize the photo process.
U.S. Pat. No. 5,633,505 of Chung et al., commonly assigned, for "Semiconductor Wafer Incorporating Marks for Inspecting First Layer Overlay Shift in Global Alignment Process" relates to overlay inspection.
See the Morita et al. reference "Impacts of Reticle and Wafer Elasticity Control on Overall Alignment Management Strategy", SPIE Vol. 3334, pp 510-518, 0277-786X/98.
U.S. Pat. No. 5,841,144 of Cresswell for "Overlay Target and Measurement Procedure to Enable Self-Correction for Wafer-Induced Tool-Induced Shift by Imaging Sensor Means" discusses in the abstract "test structure elements . . . with one component of each spaced at progressively greater distances from an arbitrary baseline, such that a zero overlay element may be identified by the alternative imaging senor means".
U.S. Pat. No. 5,879,866 of Starikov et al. for "Image Recording Process with Improved Image Tolerances Using Embedded AR Coatings" discusses self-correction of overlay using antireflective materials.
In the current state of the art, the optical stepper exposure sequence depends only on the level at which the sensor can work on the dies to be exposed or can not work on the dies because of distortion problems related to expansion generated by heating of elements of the system which leads to misalignment. Thus there a is need to solve this distortion problem.